Method of crankshaft construction



Dec. I5, 1953 B. NELSON 2,662,267

METHOD OF CRANKSHAFT cousmucnon Filed Nov. 1, 1947 INVENTOR BARNEY NELSON ATTORNEY Patented Dec. 15, 1953 UNITEDSTATES ;ATENT OFFICE 2 Claims.

This invention relates to crankshafts, as crankshafts for internal combustion engines andthe like, and has particular reference to an improved and highly effective process or method of constructing crankshafts.

In the formation of crankshafts, especially those of comparatively heavy, multi-crank character for multi-cylinder engines and the like, it has been the practice heretofore in many instances, to form the crankshaft by a forging process wherein the forged cranks and throws are relatively angularly related by twisting each throw into the proper position. Such process of throw positioning frequently results in a weakened crankshaft structure, consequent to the tension and twist stresses set up therein, particularly in the zones of juncture of the shaft and throws and in the shaft journal or hearing sections between the throws. Accordingly, it is the principal purpose of the present invention to provide a method of crankshaft construction. in which the desired predetermined relative angular relationship of the crank throws is attained without resort to twisting as is now done, whereby there is avoided shaft weakening of the character above expressed.

Objectively to the foregoing purpose-of the invention, the improved method as now provided, includes forming a forged crankshaft billet to have a plurality of distinct or outstanding sections of substantially uniform size and wherein the sections are concentric of the longitudinal shaft axis, thence producing a reference surface on each section, with the referencesurface of one section'having a predetermined angular relation to that of an adjacent section, as in accordance with the desired angular relationship of the crank throws to be formed, thence forging the sections individually, such as to extend each laterally of the shaft in a direction normal to the reference surface of the section, and thereafter reducing each section to afford distinct crankarms and a connecting crank pin.

Other objects and advantages of the present improvements will appear readily from the following description of the invention. The several stages of the process of crankshaft formation are illustrated in the accompanying drawing wherein:

Fig. 1 shows a rough forged crankshaft billet to which is applied the present method of crankshaft formation;

Fig. 2 illustrates the forged billet of Fig. 1 reduced or machined to afford a series of outstanding sections, providing the elements which ultimately will appear in the form of crank throws;

Fig. 3 illustrates the forged structure of Fig. '2, but with each of the outstanding sectionsreduced in one face portion thereof to afford a reference surface;

Fig. '4 is a sectional view transversely of the structure of Fig. 3 as viewed from line 4-1; in Fig. 3;

Fig. 5 illustrates somewhat diagrannnatically and in enlarged view, the relative angular position'of the reference surfaces provided on the outstanding sections as appears in Fig. 3;

Fig. fishows the-shaft'structure of 'Fig. 3 following the forging'cperation on the outstanding shaft sections thereof, illustrating the extension of each section laterally'of the shaft in a direction normal to its reference surface;

Fig. 7 is an enlarged end elevation of the forged shaft of Fig. 6 as appears from line 1-7 in the latter figure;

Fig, 8 is an enlarged fragmentary view of the finished crankshaft, illustrating the crankarms and connecting crankpin resulting from machining of the extended shaft sections, and

Fig. 9 is an end elevation of the shaft structure shown-in Fig. 8.

Referring to thedrawing by suitable characters ofreference, Fig. 1 illustrates a one-piece, rough forged shaft billet E8, the length and diameter of the portion ll thereof between the flange l2 and shoulder it being such as to afiord sufiicient metal for forming the desired or requirednumber of crank throws. While the shaft billet shown is of "circular section by preference, it is to be understood that the billet may he of any other sectional shape, as square, octagonal, hexagonal,

etc.

In accordance with the presently improved method of crankshaft formation, the shaft billet of Fig. 1 in the length ll thereof, is reduced, as by machining, such as to provide alternate outstanding ,and recessed sections I5 and I6 respectively, concentrically of the longitudinal shaft axis. The outstanding sections I 5 are of uniform size and may be equally relatively spaced lengthwise of the shaft, as shown, or otherwise either or both end faces thereof, to facilitate the formation of a reference surface thereon for a later operation in the present process. For example, the end section a at the right hand end of the shaft shown in Fig. 2, has a line [9 (Fig. 5) inscribed along its end face l8 (Fig. 2), such line being a chord line normal to a shaft radius. The section is then reduced as by flame cutting or otherwise, to afford a planar face 20a (Figs. 3 and 5) coincident with the chord line l9, such planar face providing a reference surface so located as to be normal to the intended direction of the crank throw to be formed from the section. In a similar manner, the next and each of the remaining sections is provided with a reference surface, the surfaces of the several sections a through 3' being here designated by the reference characters Zila through 207'. These surfaces are relatively angularly related to each other as indicated in Figs. 3 and 5, in accordance with the desired relative angular relationship of the crank throws to be formed from the sections.

After reduction or fiame cutting of the sections at through 7' to afford the reference surfaces Zfia et seq., the shaft billet is placed in a furnace and heated to the proper forging temperature according to usual forging requirements. Thereafter, the billet is disposed in a forging unit of any suitable type, as a steam hammer, drop hammer, hydraulic press, steam hydraulic press or the like. In the forging process, the sections are treated individually, that is, one section as a is forged, followed by forging of the next adjacent section b and so on through the series of shaft sections. in the forged unit, a section [5 is located such that its reference surface is at a right angle to the face of the forging die, and relatively adjacent one wall of the die, from which it will appear that the section l5 will be extended laterally from the shaft, resulting in the projection of the section as illustrated in Figs. 6 and 'I, and the reference surface will be substantially retained in limiting abutting contact with the wall of the die to prevent appreciable displacement of the reference surface from the axis of the shaft billet. Each of the sections l5 are so forged individually, and in each case such that the lateral extension thereof occurs in a direction normal to its reference surface. here that in the instance of a relatively long shaft embodying a large number of throws, the shaft billet may have to be reheated one or more times during the forging of the sections l5. Care must be taken of course, in properly locating each section in the die before forging, as well as in maintaining its position during the forging operation, so as to assure the lateral extension of the section in a direction normal to its; reference surface or as nearly normal thereto as is practically possible. The resulting extended sections are indicated in the end view of Fig. '7, in the relative angular positions predetermined according to the desired crank angles, with each thereof peripherally defined by opposite flat faces ill and arcuate sides 22 (Figs. 6 and 7). 7

Following the forging process as above described, the crankshaft is then machined in each of the extended sections 15 to form distinct crank arms 25 and connecting crank pin 26 (Fig. 8).

The result of the now described process of crankshaft formation, is that sections a through a from In placing the billet 9 It may be noted which the crank throws are formed, are relatively angularly related in the forging process, in accordance with the desired angular relationship of the throws. thereby avoiding the requirement as has heretofore prevailed, of twisting each throw section into its correct position. Accordingly, a crankshaft formed as now described, will be much stronger in all zones thereof, since there is here avoided tension and twist, stresses in the crankshaft as such appear consequent to the older practice of crankshaft formation.

Having now described a presently preferred embodiment of the invention, it is to be understood that the method or process as disclosed, may be modified without departing from the spirit and full intended scope of the invention as defined by the claims.

I claim:

1. The method of forming a crankshaft in a die having an internal wall which comprises,

providing a one-piece shaft billet having distinct sections of substantially uniform size, cutting a planar reference surface on each section in a plane normal to a radius of the shaft so that the reference surface of each section is disposed closer to the longitudinal axis of the shaft than the diametrically opposed surface of that section, the reference surface of the sections being relatively angularly related according to the relative angular relationship predetermined for the crank throws, disposing the sections one at a time in the forging die such that the reference surface of the section is adjacent to and parallel with the internal wall of the die and parallel to the direction or the forging pressure, forging the section to retain the reference surface in limiting abutting contact with the wall of the die and at a constant radial distance from the center line of the billet and to extend that portion of the section on the opposite side of the shaft from said reference surface in the direction normal to the plane of its reference surface, and machining each extended section to provide distinct crank arms and a comiecting crank pin.

2. In a method of forming a crank-throw on an elongated, generally cylindrical metal crankshaft blank having a central axis, the steps of cutting a reference surface on a crank-throw section of the blank at one side of the axis and parallel to a plane through the axis so that the reference surface is disposed closer to the central axis than the diametrically opposed surface of the blank, displacing a portion of the metal about said axis a predetermined distance in a direction diametrically away from said reference surface to the other side of said shaft axis while holding the reference surface against displacement from the central axis and machining said displaced metal on the crank-throw section of the blank to form crank arms and a connecting crank pin.

EARNEY NELSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,290,324 Groene et al. July 21, 1942 FOREIGN PATENTS Number Country Date 332,666 France June 5, 1903 592,473 Germany Jan. 25, 1934 

